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1. Field of the Invention
The invention relates generally to the field of integrated circuit fabrication. More particularly, the invention relates to the installation and centering of a polishing pad on a Chemical Mechanical Process (CMP) polishing machine using a centering apparatus.
2. Description of the Related Art
After circuitry has been burned into a silicon wafer containing a number of potential integrated circuit chips, an oxide layer is applied to the surface of the wafer. The oxide layer protects and insulates the circuitry. xe2x80x9cHolesxe2x80x9d are etched in the oxide layer to circuit connection points and metal interconnects are deposited thereon, and metal traces are formed of the oxide layer surface. A number of interconnect layers are necessary to make electrical connections with all of the circuitry on the wafer. Accordingly, a new oxide layer is deposited on top of the prior layer to electrically isolate the interconnects and traces. Because the topography of the surface on which each of the successive oxide layers is deposited is not planar, the resulting oxide surface is also not planar. Planarity is necessary, however, so that the next layer of metal interconnects may be deposited on the chip. To achieve the necessary planarity, a chemical mechanical process (CMP) is typically utilized.
CMP is an abrasive process using chemical slurries and a circular sanding action to polish the surface of the oxide layer smooth. Typical wafer polishers, such as the MirraMesa(trademark) by Applied Materials, Inc., have multiple rotating platens and multiple heads to hold silicon wafers, facilitating the polishing of more than one wafer simultaneously.
Prior art FIGS. 1a and 1b illustrate two views of a portion of a CMP polishing machine. A rotating platen 100 is secured to the polisher base. A polishing pad 110, such as IC1000 pads by Rodell, Incorporated of Newark, Del. made of a polymeric material is secured to the top of the platen 100 with a pressure-sensitive adhesive. The polishing pad typically has a diameter greater than the platen and accordingly, the edge of the polishing pad 110 extends beyond the edge of the platen 100. The polishing pad comprises a series of circumferential ridges and grooves 150, which carry the abrasive slurry towards the wafer 125 and carry away oxide removed from the wafer 125. A conditioning head 140 is provided that typically comprises an abrasive-encrusted (e.g. diamond, or silicon oxide) pad, which acts to roughen the surface of the polishing pad 110. The slurry, generally comprised of Silicon Oxide particles, is introduced to polishing pad 110 through a series of nozzles 135 located on a slurry deposition head 130. The wafer 125 is orientated face down and is secured to a wafer head 120, which moves vertically to bring the wafer 125 in contact with the polishing pad 110.